Excavated soil is usually required as backfill around a construction site, and the stability of the backfill is often required to equal or exceed that of the adjacent undisturbed soil. Thus, the soil of a road, runway or the like usually requires greater strength than the adjacent natural soil strength. Conventionally, with respect to these requirements, the stabilization process has been performed as follows. First, the mixture of a cementitious material, such as cement, lime, gypsum, water-glass, or the like, and the excavated soil is backfilled at the excavation site and then the backfill is compacted by rolling, tamping or the like, while solidification of the cementitious material occurs.
In this stabilization process the ratio of the cementitious material to the excavated soil is relatively small, namely less than 10%. Furthermore, in order to maximize the strength of the mixture of soil and cementitious material, it is necessary to use optimum water content. However, there are many grades of soil, some of which are not amenable to homogeneous mixing with a cementitious material and water. Even with soils relatively amenable to mixing, it has been difficult to mix soil homogeneously with a small amount of cementitious material and water.
There are two Japanese Patent Publications (B2) Nos. Sho 51-33662 and Sho 61-8212 which disclose techniques of treating excavated soil. Publication Sho 51-33662 discloses a method of treatment comprising the blending of soil, cement and sludge in a vessel installed at the construction site. As a result of this mixing, the treated soil is alleged to have the desired strength and stability. According to this method, the addition of sludge or the like is done simultaneously with the addition of cement. Publication Sho 61-8212 discloses the method of installing an excavated soil separating unit, a measuring unit and a mixing unit on the excavation site. Soil is excavated and drained of water content by the separating unit. The resultant residue, or mud, is reinforced with a cement homogeneously mixed and then backfilled into the excavation by means of a pressure pump.
However, it has been difficult to mix together the excavated soil, cementitious material and water homogeneously by either method. The strength of the solidified soil is liable to fluctuate because the physical qualities of the soil will vary from one construction site to another. For instance, in soil which contains gravel and rock, separation may occur similar to the phenomenon of separation of aggregate in concrete. Furthermore, it has also been difficult in a case of particularly soft cohesive soil to homogeneously disperse a small amount of water and cementitious material.
Previous to this application, the Applicant invented a method to prepare homogeneous, high quality mortar and concrete in which there is no separation of the aggregate and excellent workability is obtained by using small ice particles in lieu of water and then causing the gradual melting of the ice particles in the stage of mixing the cement and aggregate. (See International Laid-Open patent applications Nos. W086/00884 and W087/00163). In addition, Japanese Patent Publication (B2) No. Sho 53-005694 has disclosed a method of manufacturing construction boards, which comprises the steps of mixing a powdery hydraulic binder with crushed ice in a form like snow at a temperature below the melting point of water substantially in a dry state, compressing the resultant substantially dry mixture to a predetermined thickness and then solidifying the resultant layer at a temperature above the melting point of water. Further, this method has suggested that a porous board is manufactured by adjusting the melting of ice in the stage of solidification.
It is therefore an object of the present invention to produce treated backfill in which ice particles are used in lieu of part or all of the water required for adding to the mixture of excavated soil and cementitious material. The mixture having high homogeneity is effectively produced by making use of characteristics of ice particles in the solid phase or in the quasi-solid phase resulting from the melting of the surfaces thereof, thereby making it possible to treat the excavated soil to provide it with the desired physical properties at low cost.